Engaging in and being victimized by social aggression during adolescence confers risk for the development of psychopathology and relates to emerging antisocial behavior. Understanding the development and consequences of social aggression may clarify the role of gender in emerging mental disorders, because girls engage in more social than physical aggression and social aggression might contribute to the development of disorders for which girls and women have higher base rates (depression, eating disorders, and borderline personality features, Crick et al., 1999, Crick & Zahn-Waxler, 2003). Social aggression harms peers by damaging friendships or social status, and includes behaviors such as social exclusion (verbal or nonverbal), malicious gossip, and friendship manipulation (Cairns, Cairns, Neckerman, Gest, & Gariepy, 1989; Galen & Underwood, 1997; Underwood, 2003). This investigation examines the development of social and physical aggression through late adolescence, to explore the growth, change, and sequelae of engaging in and being the victim of social and physical aggression for an age range in which social aggression has rarely been studied (ages 14 [unreadable] 18). This competing continuation application proposes to follow the same sample that has been studied since age 9 in the previous project ([unreadable]Social Aggression: Precursors and Outcomes[unreadable], 2 R01 MH063076-06). For the most complete understanding of social aggression, this research will include measures of engaging in and being victimized by social aggression. An important innovation of this phase of the longitudinal study will be careful assessment of social aggression in online communication by providing adolescents with handheld devices and recording and coding the content and social processes of their Instant Messaging, text messaging, and email communication. This investigation will use multiple methods to measure social aggression in different contexts (coding of online communication and text messaging, self-reports via telephone interviews, friend reports, parent reports, and teacher and activity leader reports) to examine growth and change in mean levels of social and physical aggression for the total sample, as well as to examine whether individuals follow different types of trajectories for engaging and being the victim of social aggression. This research will examine how growth and change in social aggression relates to the emergence of psychopathology and antisocial behavior. Fully understanding developmental psychopathology for both genders demands serious investigation of engaging in and experiencing social aggression. This study will explore developmental precursors of adolescent psychopathology, with the long-term goal of determining whether reducing social aggression might be helpful in preventing externalizing symptoms, internalizing problems, personality disorders, and eating disorders.